Divergent carbon dynamics under climate change in forests with diverse soils, tree species, and land use histories

Abstract

Abstract. Accounting for both climate change and natural disturbances-which typically result in greenhouse gas emissions-is necessary to begin managing forest carbon sequestration. Gaining a complete understanding of forest carbon dynamics is, however, challenging in systems characterized by historic over-utilization, diverse soils and tree species, and frequent disturbance. In order to elucidate the cascading effects of potential climate change on such systems, we projected forest carbon dynamics, including soil carbon changes, and shifts in tree species composition as a consequence of wildfires and climate change in the New Jersey pine barrens (NJPB) over the next 100 years. To do so, we used the LANDIS-II succession and disturbance model combined with the CENTURY soil model. The model was calibrated and validated using data from three eddy flux towers and the available empirical or literature data. Our results suggest that climate change will not appreciably increase fire sizes and intensity. The recovery of C stocks following substantial disturbances at the turn of the 20th century will play a limited but important role in this system. In areas characterized by high soil water holding capacity, reduced soil moisture may lead to lower total C and these forests may switch from being carbon sinks to becoming carbon neutral towards the latter part of the 21st century. In contrast, other areas characterized by lower soil water holding capacity and drought tolerant species are projected to experience relatively little change over the next 100 years. Across all soil types, however, the regeneration of many key tree species may decline leading to longer-term (beyond 2100) risks to forest C. These divergent responses were largely a function of the dominant tree species, and their respective temperature and soil moisture tolerances, and soil water holding capacity. In summary, the system is initially C conservative but by the end of the 21st century, there is increasing risk of de-stabilization due to declining growth and regeneration.

Decadal-Scale Reduction in Forest Net Ecosystem Production Following Insect Defoliation Contrasts with Short-Term Impacts of Prescribed Fires

“…Similarly, predicting the impact of invasive insects on long-term forest C dynamics using process-based simulation models has been only partially successful. Although process-based models have accurately captured the effects of gypsy moth defoliation on tree biomass, stand species composition, and the dynamics of GEP and ANPP, they have generally underestimated the long-term reduction in NEP in forests of the PNR following disturbance [9][10][11]. For example, the Ecosystem Demography 2 Model parameterized for xeric hardwoods and conifers and to represent defoliation events and tree mortality at oak-dominated stands in the PNR over 200-year simulations indicated that defoliation intensity was linearly related to decreases in annual NEP, but also predicted that post-disturbance NEP exceeded 80 to 90 g C m −2 year −1 at all levels of defoliation [11].…”

“…Since abandonment, these regenerating forests have been moderate to strong sinks for atmospheric carbon dioxide (CO 2 ) [3][4][5][6][7]. In the mid-Atlantic region, estimates of net primary production (NPP) and net ecosystem production (NEP) for intermediate-age forests are highest for oak-hickory forests and lowest for pine-dominated forests [8][9][10]. Overall NEP has been projected to decline slowly as forests age across the region [1, 9,11,12], with productivity declining more slowly for hardwood-dominated forests than conifer-dominated forests [5,9,10].…”

“…In the mid-Atlantic region, estimates of net primary production (NPP) and net ecosystem production (NEP) for intermediate-age forests are highest for oak-hickory forests and lowest for pine-dominated forests [8][9][10]. Overall NEP has been projected to decline slowly as forests age across the region [1, 9,11,12], with productivity declining more slowly for hardwood-dominated forests than conifer-dominated forests [5,9,10]. These intermediate-age forests now experience disturbance regimes dominated by wind and ice storms, insect damage, and managed wildland fire that differ in temporal and spatial scales and intensity compared to past stand-replacing disturbance such as intensive timber management or large wildfires [6,[13][14][15][16].…”

Impacts of fire and climate change on long-term nitrogen availability and forest productivity in the New Jersey Pine Barrens

“…3) of LANDIS-II to simulate tree establishment, forest succession, and C and N cycling ( Fig. 2; Scheller et al 2011aScheller et al , 2012. This succession extension uses species-specific life history attributes and growth rates to model tree growth and regeneration, which helps determine successional changes in species composition.…”

“…The extension also simulates N leaching (dependent on precipitation, soil characteristics, and hydrologic flow rates) and denitrification, which is a function of available N (Scheller et al 2012). The extension also simulates the internal cycling of C and N through the vegetation (leaf, wood, fine roots, and coarse roots by species and age), detritus (foliar, woody, fine roots, and coarse roots), and soil (fast, slow, and passive pools) (Scheller et al 2011a(Scheller et al , 2012. The decomposition of C and mineralization of N is calculated separately in each of the detrital and soil pools.…”